Traversing a hierarchical layout template

ABSTRACT

Methods and apparatus implementing systems and techniques for traversing a hierarchical layout template to accelerate a constraint-driven backtracking search for a solution of the layout template. In general, in one implementation, the techniques include identifying a shared content element constraint that defines a content requirement common to all layout structures possible in a choice substructure in a hierarchical layout template, and associating the shared content element constraint with a root node of the choice substructure in the hierarchical layout template. In another aspect, the techniques include receiving content elements to be presented according to a hierarchical layout template that includes a choice substructure including a root node having a shared content element constraint that defines a content requirement common to all layout structures possible in the choice substructure, and traversing the hierarchical layout template to generate a layout structure that accommodates the content elements, said traversing including traversing the hierarchical layout template based at least in part on the shared content element constraint associated with the root node.

BACKGROUND OF THE INVENTION

The present application describes systems and techniques relating toelectronic document layout, for example, traversing a hierarchicallayout template.

In the publishing field, various techniques are used to improve the pagelayout process. Page layout involves creating a visual presentation withappropriate formatting for a document given input content for thedocument. For example, a FrameMaster Page is a standard HTML (Hyper TextMarkup Language) file that contains code for managing control parametersof a Web page layout. Example control parameters include parameters thatcontrol screen width percentage, shape of a footnote region,resizability, and scroll bars.

Additionally, various layout templates may be created using existingsoftware products. A layout template describes available layoutstructures for a page layout, such as a graphics frame that specifieswhere a picture goes on a page. QuarkXPress™ and InDesigne® are bothexample software products, available from Adobe Systems Incorporated ofSan Jose, Calif., that enable creation of layout templates. Typicallayout templates can expect certain types of content and leave holes inthe page layout if the expected content is not present.

Interscript is a specification that enables creation of flexible layouttemplates. The Interscript Specification was originally developed andavailable from Xerox Corporation of Stamford, Conn. At a first level,Interscript is a document interchange encoding that has a simple syntaxand semantics that can be interpreted readily, even by low-capabilityeditors. Interscript is a basic document description language with asmall core and an extension-by-definition facility that allows creationof dynamic layout templates.

An Interscript template is an example of a hierarchical layout templatethat describes possible layout structures and potential aspects of alayout. The final page layout created from an Interscript template canbe made to depend on the content that is poured into the template; thus,holes need not be left in the page layout when certain expected contentis not present. Moreover, Interscript enables creation of hierarchicallayout templates that can include features for improved layout scalingand can include layout penalties for improved layout selection (e.g., acolumned document template may have a penalty on the height of the boxcontaining the columns, thereby balancing the columns on a half-fullpage).

SUMMARY OF THE INVENTION

In general, in one aspect, the invention involves identifying a sharedcontent element constraint that defines a content requirement common toall layout structures possible in a choice substructure in ahierarchical layout template, and associating the shared content elementconstraint with a root node of the choice substructure in thehierarchical layout template. In another aspect, the invention involvesreceiving content elements to be presented according to a hierarchicallayout template that includes a choice substructure including a rootnode having a shared content element constraint that defines a contentrequirement common to all layout structures possible in the choicesubstructure, and traversing the hierarchical layout template togenerate a layout structure that accommodates the content elements, saidtraversing including traversing the hierarchical layout template basedat least in part on the shared content element constraint associatedwith the root node.

Advantageous implantations of the invention include one or more of thefollowing features. Identifying the shared content element constraintcan involve automatically identifying, such as in a programmablemachine, one or more content constraints in one or more leaf nodes ofthe choice substructure in the hierarchical layout template, anddiscovering commonality in the one or more content constraints in thechoice substructure. The invention can involve creating the hierarchicallayout template, such as by creating a data structure or creatingstructured text-based data. The invention can involve obtaining thehierarchical layout template, such as by loading an Interscript layouttemplate, or loading structured text-based data, and generating thehierarchical layout template from the structured text-based data.

Traversing the hierarchical layout template can involve comparing atleast one of the content elements with the shared content elementconstraint associated with the root node to avoid traversing at least aportion of the choice substructure. Traversing the template can involveselecting among template choices in the hierarchical layout template,and generating the layout structure based on the selected templatechoices. Traversing the template can involve generating a preferredlayout based on penalty values associated with selected layoutsubstructures.

In another aspect, the invention features a hierarchical layout templatestorable on a machine-readable medium, the hierarchical layout templateincluding template leaf nodes each having one or more content elementconstraints each defining for an associated leaf node a contentrequirement for a layout structure using the associated leaf node, and achoice substructure including a root node and at least one of thetemplate leaf nodes as a descendent of the root node, the root nodehaving an associated shared content element constraint that defines acontent requirement common to all layout structures possible in thechoice substructure. The template can include additional leaf nodeswithout content element constraints. The hierarchical layout templatecan be stored as a data structure, an Interscript layout template,and/or structured text-based data (e.g., linearized text-based treedata, (Extensible Markup Language) XML data).

The shared content element constraint can be incorporated in the rootnode, and the shared content element constraint can define a negativecontent requirement common to all layout structures possible in thechoice substructure in the hierarchical layout template. The sharedcontent element constraint can be an abstracted constraint derived froma plurality of content element constraints, and the shared contentelement constraint can be a complex content element constraint.

The invention can be implemented to realize one or more of the followingadvantages. Time performance can be improved for generation of a layoutstructure from a hierarchical layout template, given received content tobe presented according to the hierarchical layout template. Aconstraint-driven backtracking search for a solution of the hierarchicallayout template can be accelerated by avoiding choices that will resultin dead ends due to the nature of the content being presented using thetemplate. Traversal of the hierarchical layout template can beaccelerated, and backtracking can be minimized.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features andadvantages of the invention will become apparent form the description,the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example hierarchical layout template.

FIG. 2 shows an example data structure for a hierarchical layouttemplate.

FIG. 3 shows three layout structures taken from the potential layoutstructures of the hierarchical layout template of FIG. 1.

FIG. 4 is a flow chart illustrating creation of a layout structure forcontent using a hierarchical layout template and a shared contentelement constraint.

FIG. 5 is a flow chart illustrating creation of a shared content elementconstraint in a hierarchical layout template and creation of a layoutstructure for content using the hierarchical layout template and theshared content element constraint.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows an example hierarchical layout template 100. Thehierarchical layout template 100 includes nodes A-J arranged in ahierarchy that describes possible layout structures (e.g., a completepage layout possibility-space). Each node A-J describes a potentialaspect of a layout. Thus, the nodes A-J can include page nodes,generalized container nodes, section nodes, paragraph nodes, figurenodes, table nodes, column nodes, line nodes, character nodes, and othertypes of nodes that can be included in an electronic document layout,including template processing control nodes.

The nodes are labeled A through J for ease of reference. In practice,the nodes in a hierarchical layout template do not require names,although frequently many of the nodes in a hierarchical layout templatehave explicit or implicit names. Unlike a DTD (document typedefinition), the hierarchy in a hierarchical layout template can beincorporated into the template itself and need not rely on namingconventions. This provides added flexibility in that nodes of the sametype (e.g., figure nodes) need not have identical definitions.

Each node A-J can be defined at the same location in the template as thenode itself, at another location, and/or partially at both suchlocations. Additionally, each node A-J can include an associated contentelement constraint. A content element constraint defines a piece ofcontent, such as a figure, a photograph or a hyperlink, that is requiredby the associated node.

The hierarchical layout template 100 is an electronic document that canbe used to generate a layout structure to format content to produceanother electronic document (e.g., a work processing document, a Webpage document, or a final format document) that marries layout andcontent. As used herein, the terms “electronic document” and “document”mean a set of electronic data, including both electronic data stored ina file and electronic data received over a network. An electronicdocument does not necessarily correspond to a file. A document may bestored in a portion of a file that holds other documents, in a singlefile dedicated to the document in question, or in a set of coordinatedfiles.

A final format document generally provides a device-independent formatfor publishing and/or distributing electronic documents. Thus, a finalformat document is conventionally a file that lies between a layoutprogram and the typical raster image processors, which drive traditionalprinting apparatus. An example of a final format is the PortableDocument Format (PDF) available from Adobe Systems Incorporated of SanJose, Calif. Example software for creating and reading PDF documents isthe Acrobat® software, also of Adobe Systems Incorporated. The Adobe®Acrobat® software is based on the Adobe® PostScript® technology whichdescries formatted pages of a document in a device-independent fashion.

The hierarchical layout template 100 can be stored in many differentforms and formats and can conform to various layout template standards.The hierarchical layout template 100 can be stored as a data structure(e.g., a tree data structure), and/or as a structured text-baseddocument. The hierarchical layout template 100 can be text-basedlinearized tree data, such as XML data. The hierarchical layout template100 can be an Interscript document. Interscript is a public-domainstandard defining a digital representation of editable documents. Asused herein, the term “text” means character data encoded using anystandardized character encoding scheme, such as Unicode or ASCII(American Standard Code for Information Interchange).

FIG. 2 shows an example data structure 102 for the hierarchical layouttemplate of FIG. 1. The example data structure 102 is a tree datastructure where choices in the hierarchical layout template have beenconverted into corresponding choice nodes 105, NULL nodes 110 andexpandable nodes 115, 120 (e.g., a JxN node represents one or more Jnodes). Other structures are also possible. Leaf nodes 120, 125 can eachinclude a content element constraint, as in a typical hierarchicallayout template. In addition, non-leaf nodes 115, 130 can each include ashared content element constraint.

A shared content element constraint defines a content requirement commonto all layout structures possible in a choice substructure in ahierarchical layout template. A content element constraint can be aplural constraint (e.g., three separate pieces of content are eachrequired). For example, if node E has two content requirements (e.g., afigure and a caption), node E has a plural content element constraint.Likewise, the node B can have a plural shared content element constraintbecause a choice substructure 150, of which node B is the root, has theplural content element constraint from node E common to all possiblelayout structures. Any layout structures that includes a node B willalso include a node E because of the structure of the hierarchicallayout template.

A shared content element constraint defines a content requirement commonto all layout structures possible in a choice substructure. The contentrequirement can be singular, plural or complex. A shared content elementconstraint can be a content constraint promoted from one of the leafnodes (e.g., a single content constraint identified in a single leafnode), and/or an abstracted constraint derived from one or more contentconstraints found in the leaf nodes. Identifying a common contentrequirement can be performed by a person or by a machine. A person canidentify such constraint commonality while constructing a hierarchicallayout template or when analyzing an existing hierarchical layouttemplate. A machine can identify common content element constraints inan existing hierarchical layout template as part of an automatedprocess.

This identification process can involve, for each leaf node in ahierarchical layout template, identifying any content elementconstraints, and then propagating those content element constraints backup the tree until no more commonality can be found. For example, if nodeE includes a content constraint (e.g., a figure is required) and node Fincludes another content constraint (e.g., a caption is required), thechoice substructure 150 includes a common content constraint, which isthe content constraint from node E (e.g., a figure is required). Thiscommon content constraint can be stored as a shared content elementconstraint in node B. If node H includes a content constraint, a choicesubstructure 155 includes this common content constraint, which can bestored as a shared content element constraint in node C.

Moreover, a shared content element constraint can be complex (e.g., thecommonality among layout structures can include alternativeconstraints). For example, if node I includes a content constraint(alpha) and node J includes a content constraint (beta), node 115 canhave a complex shared content element constraint (for each node D, onealpha or at least two betas) associated with the root node 115 of achoice substructure 160.

Although FIG. 2 illustrates a hierarchical layout template in the formof a tree, the hierarchical layout template is not a typical tree inthat multiple alternative trees are represented by the template tree;the choices in the template have not been made. The hierarchical layouttemplate represents all possible layout structures, and a resultinglayout structure is produced by selecting nodes from the hierarchicallayout template. Thus, a resulting layout structure can also be a tree.FIG. 3 shows three layout structures 210, 220, 230 derived from thepotential layout structures of the hierarchical layout template ofFIG. 1. As can be seen in FIGS. 2 and 3, the choice substructure can beeither wide or narrow and still benefit from a shared content elementconstraint placed at its root.

With shared content element constraints in place in the hierarchicallayout template, generation of a layout structure from the template canbe improved. During traversal of the hierarchical layout template,backtracking can be minimized. A constraint-driven backtracking searchfor a solution of the hierarchical layout template can be accelerated byavoiding decisions that will result in dead ends due to the nature ofthe content being poured into the template. The layout structure thatresults from pouring the content into the template can be generated morequickly by comparing elements of the poured content with shared contentelement constraint(s) at non-leaf node(s) in the hierarchical layouttemplate.

FIG. 4 is a flow chart illustrating generation of a layout structure forcontent using a hierarchical layout template and a shared contentelement constraint. The hierarchical layout template can be structuredtext-based data (e.g., XML data), a data structure, and/or Interscriptdata. The hierarchical layout template includes a choice substructureincluding a root node having an associated shared content elementconstraint. The shared content element constraint can be a singleconstraint, a plural constraint, a complex constraint, or a negativeconstraint (e.g., absence of a particular content element is required).

The hierarchical layout template is either created or obtained at 300.Content is received at 310. The content includes content elements to bepresented according to the hierarchical layout template. Thehierarchical layout template is traversed to generate a layout structurethat accommodates the content elements at 320. Traversal of thehierarchical layout template is based at least in part on the sharedcontent element constraint.

Comparing the received content elements with the shared content elementconstraint during traversal of the hierarchical layout template allowstraversal of the choice substructure to be skipped when the contentrequirements for that choice substructure are not in place. This canreduce the amount of time needed to traverse the hierarchical layouttemplate since backtracking caused by poor template choices can beminimized. Thus, a constraint-driven backtracking search for a solutionof a hierarchical layout template can be accelerated.

FIG. 5 is a flow chart illustrating creation of a shared content elementconstraint in a hierarchical layout template and generation of a layoutstructure for content using the hierarchical layout template and theshared content element constraint. A hierarchical layout template iscreated or obtained at 400. The hierarchical layout template can haveone or more different formats and can conform to various layout templatestandards as described above. The hierarchical layout template can beobtained, such as by loading a data structure, loading an Interscriptlayout template, and/or loading structured text-based data andgenerating the hierarchical layout template from the structuredtext-based data.

The hierarchical layout template can be created by a programmablemachine and/or by a person. For example, the hierarchical layouttemplate can be created by a programmable machine, using the techniquesdescribed below, as a person supplies data defining the layout template.This supplied data can be text data, such as “{up to N lines, thenphoto; up to N lines}”, which can be used, with an additional constrainton height, to express a choice for placing a photo in a column layoutwhere the photo, if present, should be at the bottom.

One or more shared content element constraints are created at 405. Theshared content element constraint(s) can be created by a person, by aprogrammable machine operating on an existing hierarchical layouttemplate, or by a programmable machine operating on data supplied by aperson. For example, a programmable machine can identify one or morecontent constraints in one or more leaf nodes of the hierarchical layouttemplate as it is being created, and commonality in the identifiedcontent constraint(s) can be discovered in a choice substructure tocreate a shared content element constraint for the choice substructure.In the column layout example mentioned above, the “up to N lines, thenphoto” is shorthand for a sequence of choices {0 lines, then photo; 1line, then photo; 2 lines then photo; . . . ; N lines then photo}. Aprogrammable machine can create a shared content element constraint forthe choice substructure corresponding to the {up to N lines, thenphoto}, where the shared content element constraint indicates thatfollowing this choice path requires a photo.

In an Interscript implementation, content constrains that aretraditionally only associated with a mold node can be associated withchoice nodes that are higher in the hierarchical layout template. Theprocedure(s) that allow content (e.g., a store) to be poured into thehierarchical layout template can be modified to check for contentconstraints at choice nodes, and to skip over potential template choiceswith content constraints that cannot be satisfied given availablecontent.

The shared content element constraint(s) are associated with appropriatechoice substructures at 410. For example, a shared content elementconstraint can be added to a root node of a choice substructure.Alternatively, an additional choice node can be added to thehierarchical layout template to store the shared content elementconstraint. The hierarchical layout template, with associated sharedcontent element constraint(s), can be used immediately or stored forlater use.

Content to be presented according to the hierarchical layout template,with associated shared content element constraint(s), is received at415. The hierarchical layout template is traversed to generate a layoutstructure that accommodates the content elements. This traversalincludes comparing the received content with the shared content elementconstraint(s) at 420, selecting among template choices at 425, andconstructing a layout structure at 430. Comparing the content elementswith the shared content element constraint(s) allows a programmablemachine to avoid traversing at least a portion of a choice substructurein the hierarchical layout template when content requirements are notmet. Thus, this comparing can affect the selection of template choicesfrom the hierarchical layout template.

Constructing the layout structure can involve determining a preferredlayout based on penalty values associated with selected layoutsubstructures. Thus, multiple template choices can be selected based onthe received content elements and the shared content elementconstraint(s), and these selected template choices can be compared todetermine a preferred layout structure.

The invention can be implemented in digital electronic circuitry, or incomputer hardware, firmware, software, or in combinations of them.Apparatus of the invention can be implemented in a computer programproduct tangibly embodied in a machine-readable storage device forexecution by a programmable processor; and method steps of the inventioncan be performed by a programmable processor executing a program ofinstructions to perform functions of the invention by operating on inputdata and generating output. The invention can be implementedadvantageously in one or more computer programs that are executable on aprogrammable system including at least one programmable processorcoupled to receive data and instructions from, and to transmit data andinstructions to, a data storage system, at least one input device, andat least one output device. Each computer program can be implemented ina high-level procedural or object-oriented programming language, or inassembly or machine language if desired; and in any case, the languagecan be a compiled or interpreted language. Suitable processors include,by way of example, both general and special purpose microprocessors.Generally, a processor will receive instructions and data from aread-only memory and/or a random access memory. Generally, a computerwill include one or more mass storage devices for storing data files;such devices include magnetic disks, such as internal hard disks andremovable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM disks. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

To provide for interaction with a user, the invention can be implementedon a computer system having a display device such as a monitor or LCDscreen for displaying information to the user and a keyboard and apointing device such as a mouse or a trackball by which the user canprovide input to the computer system. The computer system can beprogrammed to provide a graphical user interface through which computerprograms interact with users.

The invention has been described in terms of particular embodiments.Other embodiments are within the scope of the following claims. Forexample, the steps of the invention can be performed in a differentorder and still achieve desirable results.

1. A method comprising: identifying a shared content element constraintthat defines a content requirement common to all layout structurespossible in a choice substructure in a hierarchical layout template; andassociating the shared content element constraint with a root node ofthe choice substructure in the hierarchical layout template; wherein thecontent requirement common to all layout structures possible in thechoice substructure corresponds to input content required by a node ofthe hierarchical layout template during generation of a page layoutstructure to format content to produce a document that combines layoutand content; the method further comprising: receiving content elementsto be presented according to the layout template; and traversing thelayout template to generate a layout structure that accommodates thecontent elements, said traversing including traversing the hierarchicallayout template based at least in part on the shared content elementconstraint associated with the root node; wherein said traversing thehierarchical layout template comprises generating a preferred layoutbased on penalty values associated with selected layout substructures.2. The method of claim 1, wherein said identifying the shared contentelement constraint comprises: in a programmable machine, identifying oneor more content constraints in one or more leaf nodes of the choicesubstructure in the hierarchical layout template; and in a programmablemachine, discovering commonality in the one or more content constraintsin the choice substructure.
 3. The method of claim 2, wherein saididentifying the one or more content constraints comprises identifying asingle content constraint in a single leaf node.
 4. The method of claim1, further comprising creating the hierarchical layout template.
 5. Themethod of claim 4, wherein said creating the hierarchical layouttemplate comprises creating a data structure.
 6. The method of claim 4,wherein said creating the hierarchical layout template comprisescreating structured text-based data.
 7. The method of claim 1, whereinsaid traversing the hierarchical layout template comprises comparing atleast one of the content elements with the shared content elementconstraint associated with the root node to avoid traversing at least aportion of the choice substructure.
 8. The method of claim 1, whereinsaid traversing the hierarchical layout template comprises: selectingamong template choices in the hierarchical layout template; andgenerating the layout structure based on the selected template choices.9. A software product tangibly stored on a machine-readable medium, thesoftware product comprising instructions operable to cause one or moreprogrammable processors to perform operations comprising: identifying ashared content element constraint that defines a content requirementcommon to all layout structures possible in a choice substructure in ahierarchical layout template; and associating the shared content elementconstraint with a root node of the choice substructure in thehierarchical layout template; wherein the content requirement common toall layout structures possible in the choice substructure corresponds toinput content required by a node of the hierarchical layout templateduring generation of a page layout structure to format content toproduce a document that combines layout and content; wherein theoperations further comprise: receiving content elements to be presentedaccording to the hierarchical layout template; and traversing thehierarchical layout template to generate a layout structure thataccommodates the content elements, said traversing including traversingthe hierarchical layout template based at least in part on the sharedcontent element constraint associated with the root node; wherein saidtraversing the hierarchical layout template comprises generating apreferred layout based on penalty values associated with selected layoutsubstructures.
 10. The software product of claim 9, wherein saididentifying the shared content element constraint comprises: identifyingone or more content constraints in one or more leaf nodes of the choicesubstructure in the hierarchical layout template; and discoveringcommonality in the one or more content constraints in the choicesubstructure.
 11. The software product of claim 9, wherein theoperations further comprise creating the hierarchical layout template.12. The software product of claim 11, wherein said creating thehierarchical layout template comprises creating structured text-baseddata.
 13. The software product of claim 9, wherein said traversing thehierarchical layout template comprises comparing at least one of thecontent elements with the shared content element constraint associatedwith the root node to avoid traversing at least a portion of the choicesubstructure.
 14. A method comprising: receiving content elements to bepresented according to a hierarchical layout template that includes achoice substructure including a root node having shared content elementconstraint that defines a content requirement common to all layoutstructures possible in the choice substructure; and traversing thehierarchical layout template to generate a layout structure thataccommodates the content elements, said traversing including traversingthe hierarchical layout template based at least in part on the sharedcontent element constraint associated with the root node; wherein thecontent requirement common to all layout structures possible in thechoice substructure corresponds to input content required by a node ofthe hierarchical layout template during generation of a page layoutstructure to format content to produce a document that combines layoutand content; wherein said traversing the hierarchical layout templatecomprises comparing at least one of the content elements with the sharedcontent element constraint associated with the root node to avoidtraversing at least a portion of the choice substructure; and whereinsaid traversing the hierarchical layout template comprises determining apreferred layout based on penalty values associated with selected layoutsubstructures.
 15. The method of claim 14, wherein said traversing thehierarchical layout template comprises: selecting among template choicesin the hierarchical layout template; and generating the layout structurebased on the selected template choices.
 16. The method of claim 14,further comprising obtaining the hierarchical layout template.
 17. Themethod of claim 16, wherein said obtaining the hierarchical layouttemplate comprises loading an Interscript layout template.
 18. Themethod of claim 16, wherein said obtaining the hierarchical layouttemplate comprises: loading structured text-based data; and generatingthe hierarchical layout template from the structured text-based data.19. A software product tangibly stored on a machine-readable medium, thesoftware product comprising instructions operable to cause one or moreprogrammable processors to perform operations comprising: receivingcontent elements to be presented according to a hierarchical layouttemplate that includes a choice substructure including a root nodehaving a shared content element constraint that defines a contentrequirement common to all layout structures possible in the choicesubstructure; and traversing the hierarchical layout template togenerate a layout structure that accommodates the content elements, saidtraversing including traversing the hierarchical layout template basedat least in part on the shared content element constraint associatedwith the root node; wherein the content requirement common to all layoutstructures possible in the choice substructure corresponds to inputcontent required by a node of the hierarchical layout template duringgeneration of a page layout structure to format content to produce adocument that combines layout and content; wherein said traversing thehierarchical layout template comprises comparing at least one of thecontent elements with the shared content element constraint associatedwith the root node to avoid traversing at least a portion of the choicesubstructure; and wherein said traversing the hierarchical layouttemplate comprises determining a preferred layout based on penaltyvalues associated with selected layout substructures.
 20. The softwareproduct of claim 19, wherein said traversing the hierarchical layouttemplate further comprises: selecting among template choices in thehierarchical layout template based on said comparing; and generating thelayout structure based on the selected template choices.
 21. Thesoftware product of claim 19, wherein the operations further compriseobtaining the hierarchical layout template.
 22. The software product ofclaim 21, wherein said obtaining the hierarchical layout templatecomprises: loading structured text-based data; and generating thehierarchical layout template from the structured text-based data.
 23. Ahierarchical layout template storable on a machine-readable medium, thehierarchical layout template comprising: template leaf nodes each havingone or more content element constrains each defining for an associatedleaf node a content requirement for a layout structure using theassociated leaf node; and a choice substructure including a root nodeand at least one of the template leaf nodes as a descendent of the rootnode, the root node having an associated shared content elementconstraint that defines a content requirement common to all layoutstructures possible in the choice substructure; wherein the contentrequirement common to all layout structures possible in the choicesubstructure corresponds to input content required by a node of thehierarchical layout template during generation of a page layoutstructure to format content to produce a document that combines layoutand content; wherein the hierarchical layout template is arranged tosupport traversing the hierarchical layout template comprising:comparing at least one of content element with the shared contentelement constraint associated with the root node to avoid traversing atleast a portion of the choice substructure, and determining a preferredlayout based on penalty values associated with selected layoutsubstructures.
 24. The hierarchical layout template of claim 23, furthercomprising additional leaf nodes without content element constraints.25. The hierarchical layout template of claim 23, wherein the sharedcontent element constrain is incorporated in the root node.
 26. Thehierarchical layout template of claim 23, wherein the shared contentelement constraint defines a negative content requirement common to alllayout structures possible in the choice substructure in thehierarchical layout template.
 27. The hierarchical layout template ofclaim 23, wherein the shared content element constraint comprises anabstracted constraint derived from a plurality of content elementconstraints.
 28. The hierarchical layout template of claim 27, whereinthe shared content element constraint comprises a complex contentelement constraint.
 29. The hierarchical layout template of claim 23,wherein the template leaf nodes and the choice substructure form atleast a portion of a data structure.
 30. The hierarchical layouttemplate of claim 23, wherein the template leaf nodes and the choicesubstructure form at least a portion of an Interscript layout template.31. The hierarchical layout template of claim 23, wherein the templateleaf nodes and the choice substructure form at least a portion ofstructured text-based data.
 32. The hierarchical layout template ofclaim 31, wherein the structured text-based data comprises linearizedtext-based tree data.
 33. The hierarchical layout template of claim 32,wherein the linearized text-based tree data comprises XML data.